The emerging field of social neuroscience is bridging the knowledge gap between brain mechanisms of cognition and affect and the social and motivational factors that impact interpersonal attitudes and behaviors. However, to date, the tools available for measuring social brain function have mainly restricted experimentation to recording the neural responses of an individual, confined in a scanner, to stimuli of social importance. To address this limitation we aim to develop a breakthrough hardware/software system for synchronously acquiring, analyzing, accessing and visualizing neurophysiological data from two or more participants engaged in a common activity. This low-cost, highly-automated system will enable the recording and analysis of continuous EEG and sub-second ERP signals from multiple people engaged in a social interaction. It will embody accumulated expertise about the analysis of EEG signals into automated software that will vastly reduce the labor and knowledge required to extract useful information from them. In Phase I we will implement a prototype system for simultaneously recording brain function from two people. To demonstrate feasibility, this system will be used to enable a small experiment that will utilize both highly controlled two-person computer-based tasks to study competitive interactions in a game-like context, and more naturalistic tasks that will provide data more characteristic of less structured social interactions. The resulting novel database will be used to demonstrate feasibility by testing hypotheses concerning the impact of interpersonal factors on neurophysiologic parameters, and as a resource for designing new analysis functionality for use in such multiple-person experiments. A complete, refined, data acquisition and analysis system would be implemented during Phase II and evaluated in collaborative studies with other laboratories. The outcome of Phase II will thus be a technology that will make direct, continuous measurements of brain function routinely available to scientists studying social phenomena.